1. Field of the Invention
The present invention relates to preforms, hydroforming method, and hydroformed products.
2. Description of the Related Art
A typical automobile body structural member such as a side member has a hollow structure for improving absorption capacity of crash impact, and provided with internal reinforcement members in order to reinforce the strength thereof, and a typical hydroformed product to be used as a body structural member is made by feeding hydraulic pressure to the inside of a preform having two outer members and reinforcement members to cause an inflating deformation (see, e.g., Publication No. of Unexamined Japanese Patent Application, 2004-082142).